HTTP 505 – HTTP Version Not Supported
The HTTP version used in the request is not supported by the server.
Common use case
Rare in practice, but can appear when very old or very new clients speak an HTTP version a server explicitly refuses to handle.
Example
HTTP/1.1 505 HTTP Version Not Supported
History
Part of HTTP/1.1 (RFC 2068, 1997).
Did you know?
It is one of the rarest status codes in real-world logs, since nearly every modern server and client negotiates HTTP/1.1, HTTP/2, or HTTP/3 automatically.